Magnetron electrode structure



May 9, 1961 A. D. LA RUE ETAL MAGNETRON ELECTRODE STRUCTURE 2 Sheets-Sheet 1 Filed March 28. 958

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MAGNETRON ELECTRODE STRUCTURE Filed March 28, 1958 2 Sheets-Sheet 2 [NIVE/VTORS WAY/2D flow/v/Ne 5%55327' [,4 QUE A rrog/vsv United States Patent MAGNETRON ELECTRODE STRUCTURE Albert D. La Rue, Los Altos, Calif., and Edward T. Downing, Arlington, Mass., assignors to Raytheon Company, a corporation of Delaware Filed Mar. 28, 1958, Set. No. 724,537

7 Claims. (Cl. SIS-39.65)

This invention relates generally to magnetrons and more particularly to electrode structures used in magnetron tubes.

In designing travelling wave magnetrons it is desirable to maintain the size of the electrode structure of the tube within practical limits. In the design of conventional vane-type magnetrons for use at high frequencies, the small wave lengths involved may require a large number of anode segments in order to maintain reasonable dimensions for the anode and cathode structures. Normally, this increase in the number of anode segments represents an increase in the number of resonant cavities. A large number of resonant cavities increases the difiiculty of mode separation, and also unfavorably affects the inductance-capacitance ratio of the resonant circuits so that the tuning range of the magnetron is reduced.

This invention allows the 'maintainance of practical electrode dimensions in the high frequency range without a corresponding reduction in mode separation or tunability. The invention recognizes the fact that in a vanetype magnetron the number of anode segments that are used can be chosen independently of the number of resonant cavities required. The number of anode segments can be chosen on the basis of the desired anode dimensions for the wavelength under consideration and the number of resonant cavities can be chosen solely on the necessary geometric and circuit considerations. The invention may be best described with the aid of the drawing in which:

Fig. 1 shows a longitudinal cross-sectional view taken along line 1--1 of Fig. 20f a magnetron that incorporates a particular embodiment of this invention;

Fig. 2 shows a transverse cross-sectional view of the magnetron taken along line 2-2 of Fig. l;

Fig. 3 shows a plan view of another particular embodiment of the invention; and

Fig. 4 shows a cross-sectional view of a part of the invention taken along the line 44 of Fig. 3.

The relationship between the size of the anode radius, the operating wavelength and the number of anode segments in a conventional vane-type magnetron can be expressed according to the equation r =kNx (1) in which 1', is the anode radius, N is the number of anodes, is the operating wavelength and k is a factor depending upon the geometry and the electronic efiiciency. Specifically, k can be shown to be represented according to the equation ice vide good mode separation. Secondly, the number of resonant cavities determines the inductance-capacitance ratio of the resonant system so that the larger the number of cavities, the smaller that ratio is, and the narrower the tuning range of the tube becomes.

Although mode separation and tuning range require a relatively small number of cavities, Equation 1 indicates that for high frequency operation, and, hence, small wavelength values for A, N should have a relatively large value if a reasonably practical size is to be used for the anode radius.

The invention discloses that independence can be maintained between the choice of the number of cavities and the number of anode segments. To satisfy the criteria of Equation 1 and, at the same time, to provide for good mode separation and tunability, the invention uses a large number of anode segments and a relatively small number of resonant cavities.

Figs. 1 and 2 show a typical embodiment of the invention as used in a conventional double-ring strapped magnetron. In those figures there is shown an anode structure comprising an outer anode cylinder 16 which may be of any desired material such as copper. Extending radially inward from an inner shoulder 15 of anode cylinder 16 is a plurality of anode members 5 arranged so as to form the resonant cavities 6. A conducting strap 7 is connected to alternate anode members 5, while a conducting strap 8 is connected to those intervening anode members not connected to strap 7. Between adjacent anode members 5 lie a pair of anode segments 9. The inner ends of anode members 5' and anode segments 9 are substantially equidistant from a cathode 4 centrally located along the longitudinal axis of the cylinder 16. The anode segments 9 are arranged in combination with anode members 5 so that alternate anode segments of the combination are connected to strap 7 and intervening anode segments not connected to strap 7 are connected to strap 8.

Figs. 1 and 2 also show a tuning structure comprised of capacitive tuning elements 21 that are capable of being inserted between anode vanes as shown, and inductive tuning elements 22 inserted between anode vane portions in the rear of the cavities. The operation of the tuning structure is more fully described below.

In Fig. l, the ends of the anode cylinder 16 are sealed ofi by upper and lower end plates 23 and 24, respectively. Extending through an opening in lower end plate 24 and concentric witth the axis of cylinder 16 is a lower magnetic pole piece 25. Pole piece 25 has a hole extending axially therethrough concentric with cylinder 16 through which is extended cathode cylinder 4 containing heater coil 26 that may be insulated from the cathode cylinder 4. Upper end plate 23 has therein a hole concentric with cylinder 16 through which extends an upper pole piece 27. Pole piece 27 comprises a cylinder through which extends a movable pole piece 28 having a recess 29 in its lower end which accommodates the upper end of cathode 4. Diaphragm structure 30" provides a vacuum seal between pole piece 28 and end plate 23.

Attached to the lower end of movable pole piece 28 is a tuning structure comprising a cylindrical portion 32 surrounding and attached to the pole piece 28. Extending downwardly into the cavities of the anode structure are the capacitive tuning elements 21 and the inductive tuning elements 22. The capacitive tuning elements are inserted between anode vanes 5 and 9 as shown in Fig. 2. The inductive elements are inserted in the rear portions of the resonant cavities defined by anode vanes 5. In Fig. l the capacitive elements 2.1 are shown inserted to the full extent of their travel so that maximum tuning capacitance is obtained. In this position the inductive elements 22 are substantially removed from the cavities. The oscillations of energy produced in the magnetron may be removed by the inductive coupling loop 17 which is inserted into one of the cavities 6.

The relatively large number of anodes and the relatively small number of resonant cavities, thus, assures reasonable dimensions for the anode radius as well as good mode separation. By increasing the ratio of the number of anode vanes to the number of resonant cavities, a higher inductance-capacitance ratio is obtained, thereby providing a wider tuning range. Because the increased number of vanes allows the anode structures and resonant cavities to be constructed with reasonably large dimensions at the high frequencies involved, a reasonably sized tuning structure can more easily be inserted into the capacitive and inductive regions of the cavities.

Figs. 3 and 4 show another embodiment of the invention in which the anode segments and the resonant cavities may be fabricated independently and combined in a center-strapped magnetron to provide the tube electrode structure. In Fig. 3, there are forty-eight anode members designated as the segments 19 which radially surround cathode 10. Strap 11 is connected to alternate anode segments. A cross section view looking in the direction of the arrows 44 is shown in Fig. 4. From that view it can be seen that a corresponding strap 12 is shown on the bottom portion of the structure directly below strap 11. Strap 12 is connected to the intervening anode segments that are not connected to strap 11.

Around the periphery of the anode and center strap configuration are located sixteen resonant cavities 13 which are formed by the vanes 14 that extend inwardly from the anode cylinder 18 and are radially spaced about the straps. Strap 11 is connected to alternate vanes 14, and strap 12 is connected to intervening vanes not connected to strap 11 in a manner similar to that of the anode segments as shown in Figs. 2 and 3. Such a configuration also provides the large number of anode segments necessary to obtain reasonable anode dimensions and, at the same time, the fact that fewer resonant cavities are used allows good mode separation. The oscillations of energy produced in the magnetron may be removed by the inductive coupling loop 20' which is inserted into one of the cavities 13.

The particular embodiments shown in the drawing do not represent the only embodiments of the invention. The number of anodes and the number of resonant cavities may be chosen on the basis of the particular frequency of operation and siZe desired, as long as symmetry about the cathode is maintained. Conventional vane-type magnetrons may be converted to the hybrid type of design of the invention by selecting a predetermined quantity of the total number of vanes and by removing a portion of these vanes extending to the outer periphery so as to bring about a symmetrical arrangement of resonant cavities as shown in Fig. 2. In converting a conventional vane-type magnetron in this manner into the type described by the invention, the resonant frequency will decrease by an amount depending on the number of vanes so changed. The reason for this decrease lies in the fact that the inductance of the resonant cavities has been increased while the capacitance has remained essentially constant. The conversion of an eighteen-vane X-band magnetron to an eighteen-anode segment, six-oscillator hybrid magnetron, for example, resulted in a change of resonant frequency from 10,250 mc. to approximately 9,600 mc.

A conventional vane-type magnetron may be converted into a hybrid magnetron in another way of inserting a plurality of vane segments between its already existent anode vanes. In this case, the frequency will be decreased also because the capacitance of the resonant cavities has thereby been increased while the inductance has remained essentially constant.

Accordingly the invention is not to be construed as being limited to the embodiment show in the drawing 4 and described herein except as defined by the appended claims.

What is claimed is:

1. In combination, an electron discharge device comprising an electrode structure including a cathode, a plurality of first vanes radially spaced about said cathode, said first vanes thereby constituting the sole means for defining a plurality of resonant cavities, a plurality of second vane segments radially spaced and fixedly mounted about said cathode, the number of said second vane segments being greater than the number of said first vanes, and a plurality of conducting straps connected to said first and said second vanes.

2. In combination, an electron discharge device comprising an electrode structure including a cathode, a plurality of vanes radially spaced about said cathode, said vanes thereby constituting the sole means for defining a plurality of resonant cavities, means radially spaced and fixedly mounted about said cathode between said cavity-defining vanes for increasing the capacitance of said resonant cavities, and a plurality of conducting straps connected to said cavity-defining vanes and to said capacitance increasing means.

3. In combination, an electron discharge device comprising an electrode structure including a cathode, a plurality of first vanes radially spaced about said cathode, adjacent first vanes thereby constituting the sole means for defining a plurality of resonant cavities, a plurality of second vanes radially spaced and fixedly mounted about said cathode and symmetrically spaced between each of said adjacent first vanes, said first and said second vanes thereby forming a combination of anode members radially spaced about said cathode, and a plurality of conducting members alternately interconnecting said radially spaced anode members of said combination.

4. In combination, an electron discharge device as described in claim 2, wherein said capacitance increasing means have lengths relatively shorter than said cavitydefining vanes.

5. In combination, an electron discharge device as described in claim 3, wherein said first and said second vanes are spaced equidistant from said cathode.

6. In combination, an electron discharge device comprising =an electrode structure including a cathode, a plurality of first vanes radially spaced about said cathode, adjacent first vanes thereby constituting the sole means for defining a plurality of resonant cavities, an even number of second vanes radially spaced and fixedly mounted about said cathode, pairs of said second vanes placed between each of said adjacent first vanes, said first and said second vanes thereby forming a combination of anode members radially spaced about said cathode, and a plurality of conducting members alternately interconnecting said radially spaced anode members of said combination.

7. In combination, an electron discharge device comprising an electrode structure including a cathode, a plurality of first vanes radially spaced about said cathode, a plurality of second vanes radially spaced and fixedly mounted about said cathode and said first vanes, adjacent second vanes thereby constituting the sole means for defining a plurality of resonant cavities, the number of said second vanes being less than the number of said first vanes, and a plurality of conducting members alternately interconnecting said first vanes and alternately interc0nnecting said second vanes.

References Cited in the file of this patent UNITED STATES PATENTS 2,423,161 Spencer July 1, 1947 2,632,131 La Rue Mar. 17, 1953 2,766,403 Skowron Oct. 9, 1956 FOREIGN PATENTS 507,614 ICanada Nov. 23, 1954 

